def add_setting(settings, pair):
    key, value = pair
    key = key.lower()
    value = value.lower()
    if key in settings:
        return f"Setting '{key}' already exists! Cannot add a new setting with this name."
    settings[key] = value
    return f"Setting '{key}' added with value '{value}' successfully!"

def update_setting(settings, pair):
    key, value = pair
    key = key.lower()
    value = value.lower()
    if key in settings:
        settings[key] = value
        return f"Setting '{key}' updated to '{value}' successfully!"
    return f"Setting '{key}' does not exist! Cannot update a non-existing setting."

def delete_setting(settings, key):
    key = key.lower()
    if key in settings:
        del settings[key]
        return f"Setting '{key}' deleted successfully!"
    return "Setting not found!"

def view_settings(settings):
    if not settings:
        return "No settings available."
    msg = "Current User Settings:\n"
    for key, value in settings.items():
        msg += f'{key.title()}: {value}\n'
    return msg


if __name__ == '__main__':
    test_settings = {'theme': 'dark', 'notifications': 'enabled', 'volume': 'high'}
    print(view_settings(test_settings))

